I don't see what else you can do, if its had a new map, maf and smoke tested which seems ok then I can only think its a turbo issue.

is it possible to manually operate the wastegate diaphragm valve and see what vacuum it takes to operate it over its full working distance.

The problem is where would you find any specs to know what is correct. I had an issue with a BMW turbo where the reman company had set the push rod lenght incorrect causing issues so it is possible.

Its just strange how you've gone from over boost to under boost with just a turbo change.

Also how does overboost cause turbo oil supply failure almost instantly?

Does this have a DPF, could this affect turbo performance if its restricted.